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| Titel |
Stratigraphic palaeobiology around the Pliocene-Pleistocene boundary at Altavilla Milicia (Sicily, Italy) |
| VerfasserIn |
Stefano Dominici, Marco Benvenuti, Vittorio Garilli, Alfred Uchman, Francesco Pollina |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147495
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| Publikation (Nr.) |
 EGU/EGU2017-11667.pdf |
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| Zusammenfassung |
| The Pliocene-Pleistocene around Altavilla Milicia, near Palermo (Sicily), includes a thick
siliciclastic succession rich with shell beds, dominated by molluscs, brachiopods and annelids
in fine-grained, totally bioturbated sandstones. Taphonomy of fossil assemblages indicates
the importance of taphonomic feedback and within-habitat time-averaging in proximity of
maximum flooding intervals. The trace fossil suite is characterized by the abundance of
Thalassinoides paradoxicus boxworks and by local occurence of Scalichnus, Piscichnus,
?Scolicia, ?Bichordites, Ophiomorpha, ?Gyrolithes, Palaeophycus, Diopatrichnus and
?Taenidium. These trace fossils are typical of the archetypal Cruziana ichnofacies, with local
elements of the proximal Cruziana ichnofacies, which point to deposition mainly below the
fairweather wave base. Three depositional sequences, characterized by geometries
driven by the interplay of eustatism and regional tectonics, were recognized through
sedimentary facies analysis. Biostratigraphic data frame the oldest sequence in the
upper Pliocene, whereas the thickest part of the succession, occupied by the second
sedimentary sequence, includes biozone NN16b/17 of calcareous nannoplankton
stratigraphy, thereby comprising the base of the Pleistocene. Transgressive deposits of the
third and uppermost sequence are marked by encrusted and bioeroded pebbles with
sparse oyster shells. The whole time interval is characterized by glacio-eustatic
fluctuations in the 50–100 m range and with 100 ky-periodicity. We performed a
multivariate analysis of 22 samples yielding 92 species of mollusks collected in the first
and second sequences. Clustering and ordination analysis allowed to recognize a
gradient controlled by depth-related environmental variables. At one end of the
continuum we have a very-shallow water assemblage dominated by the bivalve
Loripes orbiculatus, indicating an organic-rich seagrass bottom. Opposite in the
continuum is an offshore assemblage dominated by Corbula gibba and the extinct
gastropod Petaloconchus intortus. Both the shallowest and the deepest assemblages
are from the first (Piacenzian) sequence. The gradient at intermediate depths is
better characterized by restricting the analysis to 17 collections from the second
sequence (Piacenzian-Gelasian). The shallowest assemblage is here dominated by upper
shoreface species, such as Tellina spp. and Spisula subtruncata, and the deepest by
muddy bottom, offshore transition species, such as Venus nux, the extinct gastropod
Nassarius semistriatus and deposit-feeding nuculanoid bivalves. Plotting samples
along the composite section allows to recognize two deepening-upward trends and
two intervals of maximum flooding, in accordance with the sequence-stratigraphic
interpretation. Stratigraphic palaeobiology proves to be a powerful tool to understand
factors that control the geologic record during an interval of intense climate change. |
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